William Trager (20 March 1910 – 22 January 2005) was an American parasitologist, professor at Rockefeller University, and member of the National Academy of Sciences of the United States. Trager's research focused on developing microbiological culture systems for a variety of eukaryotic pathogens. He is best known for developing a culture system for the malaria parasite Plasmodium falciparum with James Jensen in the 1970s.